The present invention relates to a novel positive-working photoresist composition or, more particularly, to a high-sensitivity positive-working photoresist composition capable of giving a finely patterned resist layer in a high resolution and excellent in the cross sectional profile of the patterned layer and heat resistance with excellent characteristics of focusing depth latitude and exposure dose latitude even on a surface having ruggedness or level differences and high reflectivity as well as good halation-preventing effect.
As is known, the method of photolithographic patterning is a well established technology in the process for the manufacture of semiconductor devices such as ICs, LSIs and the like and liquid-crystal devices such as liquid-crystal display panels and the like. The photolithographic patterning work is conducted by first forming a layer of a so-called photoresist composition which is pattern-wise exposed to actinic rays such as ultraviolet light to form a latent image of the pattern followed by development. Of the two types of photoresist compositions including positive-working and negative-working ones, the positive-working photoresist compositions are preferred in most cases to the negative-working ones and the essential ingredients in a typical positive-working photoresist composition under practical use include an alkali-soluble resin as a film-forming ingredient and a quinone diazide group-containing compound as a photosensitizing ingredient.
The alkali-soluble resin as a film-forming ingredient in a positive-working photoresist composition most widely used in practical applications is a novolac resin in respect of the advantageous properties thereof that the resin is soluble in an alkaline aqueous solution as a developer solution without swelling to exhibit excellent developability and the resist layer formed therefrom has excellent heat resistance to withstand plasma etching with the patterned resist layer as an etching mask.
The quinone diazide group-containing compound as the photosensitive ingredient is very unique because the compound in itself has an activity to suppress the alkali-solubility of the novolac resin while, when irradiated pattern-wise with actinic rays including electromagnetic waves such as ultra-violet light, e.g., g-line and i-line, and far-ultraviolet light, e.g., excimer laser beams, and corpuscular rays for pattern-wise scanning such as electron beams, the quinone diazide group-containing compound per se is converted into an alkali-soluble form along with promotion of the alkali-solubility of the novolac resin. Thus, a great number of positive-working photoresist compositions comprising a quinone diazide group-containing compound and an alkali-soluble novolac resin and capable of exhibiting a great change in the properties by exposure to actinic rays such as electromagnetic waves and corpuscular rays have been developed and brought under practical applications (see, for example, U.S. Pat. No. 4,377,631, Japanese Patent Kokai No. 62-35349, Japanese Patent Kokai No. 1-142548, Japanese Patent Kokai No. 1-179147 and Japanese Patent Publication No. 3-4897).
Along with the increase year by year in the degree of integration in the semiconductor devices and liquid crystal devices in recent years, the accuracy required in the photo-lithographic patterning work is so fine as to be in the order of submicrons, half microns or even finer in the manufacture of, for example, VLSIs. Accordingly, the positive-working photoresist composition used therefor must satisfy several requirements that the composition can give a patterned resist layer having high resolution of the patterned images and excellent heat resistance not to cause thermal deformation in the dry etching or the post-exposure baking, i.e. heat treatment after exposure to actinic rays and before development, and that the sensitivity thereof is high in respect of the productivity along with an excellent focusing depth latitude and exposure dose latitude so as to facilitate reproduction of the resist pattern with high fidelity to the mask pattern without being affected by a level difference on the substrate surface as well as insusceptibility to halation.
As a means to accomplish the above mentioned various requirements for the performance of a positive-working photoresist composition, various attempts and proposals have been made heretofore for the admixture of the composition with various kinds of specific additive compounds. For example, Japanese Patent Kokai No. 61-141441 proposes a positiveworking photoresist composition containing a trihydroxy benzophenone having improved photosensitivity and developability though without improvement in the heat resistance of the patterned resist layer. Japanese Patent Kokai No. 61-241759 proposes admixture of the photosensitive layer formed from an esterification product of o-naphthoquinonediazide sulfonic acid and a phenol novolac resin with 1 to 20% by weight of 4,4'-dimethylaminobenzophenone, 4,4'-diethylaminobenzophenone and the like as a light-absorption agent or halation inhibitor. Such a composition has a problem that no sufficient halation-preventing effect can be obtained without greatly decreasing the photosensitivity of the composition because the additive compound per se absorbs the light of the same wavelength as that of the resist layer so that fine patterning of a half-micron order or finer can hardly be accomplished with the photoresist composition. Further, Japanese Patent Kokai No. 5-11947 discloses a positive-working photoresist composition capable of exhibiting a high halation-preventing effect by the addition of a 4-aminobenzophenone compound, 2-carboxy-4-aminobenzophenone compound or a derivative thereof to a composition consisting of an alkali-soluble resin and a 1,2-naphthoquinonediazide group-containing compound. This photoresist composition has a limitation in the resolution of fine patterns with a limiting resolution of 0.5 to 0.6 .mu.m at best not to comply with the requirements for reproduction of an extremely fine pattern.
In respect of the performance of the exposure machine, it is also a possible approach to use a lens system having a large numerical aperture by which the resolution in fine patterning could be improved. This measure, however, is not practically applicable because an increase in the numerical aperture of the lens system is necessarily accompanied by a decrease in the focusing depth latitude so that it is eagerly desired to develop a photoresist composition which is not subject to a decrease in the focusing depth latitude even by the use of a lens system of the exposure machine having a large numerical aperture.
Thus, none of the positive-working photoresist compositions in the prior art can satisfy all of the various requirements for a photoresist composition in the modern photolithographic technology.